1. Field of the Invention
The present invention relates generally to exhaust gas recirculation for internal combustion engines and, more particularly, to a method of altitude compensation of exhaust gas recirculation in an intake manifold for an internal combustion engine.
2. Description of the Related Art
Motor vehicles typically include an internal combustion engine for powering the vehicles. Commonly, these engines have an intake manifold, an exhaust manifold and an exhaust gas recirculation (EGR) system for recirculating a part of the exhaust gases from the exhaust manifold to the intake manifold for controlling emission of noxious components in exhaust gases from the engine. Currently, such an EGR system is an exhaust back-pressure controlled valve that is turned ON and OFF with an EGR vacuum solenoid. When there is back-pressure and power to the EGR vacuum solenoid, the EGR valve is opened. The EGR flow is essentially proportional to exhaust back-pressure and thus engine flow.
Barometric pressure and EGR mass flow rate decrease with increasing altitude. This decreases the actual percentage of EGR in the intake manifold. If this decrease is not compensated for, excessive fuel lean out and over spark advance will occur which can cause loss power and misfires of the engine at high altitudes. With the onset of lower tailpipe emissions and higher fuel economy regulations, there is a need in the art to provide more precise control of the EGR system.